1. Field of the Invention
The invention concerns a method of operating a broadband link, a mobile terminal, a network-side mobile radio facility, and a mobile radio system.
2. Description of the Related Art
There are two possibilities for the transmission of data between a mobile terminal and a mobile exchange with the GSM (Global System for Mobile Communication) of today. On the one hand data can be transparently transported via a connection according to the V.110 protocol with constant throughput and constant transmission time delay. On the other hand, data cannot be transparently transported at a low error rate with a packet-oriented protocol which is generally called RLP (Radio Link Protocol).
The invention begins with a possibility of realizing a broadband link to a mobile terminal, as described in the specification "European Digital Cellular Telecommunication System (FACE 2+) High Speed Circuit Switched Data (HSCSD); Stage 2 Service Description (GSM 03.34)" of the ETSI (European Telecommunication Standard Institute), September 1995.
This possibility represents a development of the above transmission mechanism. 2 to 8 radio channels are established for the broadband link to a mobile terminal, and assigned as subchannels to the broadband link. In this case the broadband link can be arranged for a transmission protocol with transparent transmission, or for one with nontransparent transmission.
With transparent transmission, data are transported in a frame structure according to the V.110 protocol, where numbers which indicate the subchannel are additionally transported in the band. In this way the data are distributed to the useful channels from the network-side entity of the transmission protocol, and are transported to the terminal-side entity in accordance with the V.110 protocol, where they are recombined by means of the subchannel numbers.
It was shown however that a broadband link which is based on this principle has a high error rate, since the recombination operates insufficiently because of the running time differences between the subchannels. Therefore, the transparent communication protocol (V.110) specified for this purpose by the relevant standard (GSM 03.34) has turned out to be unsuitable.
A modified RLP protocol is used for the nontransparent transmission, which is also called MRLP (Multiple Radio Link Protocol). The MRLP protocol distributes the data packets to the subchannels in the transmit-side entity, and recombines them in the receive-side entity by means of a transmission number. Furthermore, defective data packets are corrected in this protocol by means of an error correction process with repetition.
With broadband links based on this principle it was shown that the transmission time of the data packets is not constant because of the error correction, and the broadband link is therefore unable to fulfill the requirements of a synchronous connection. Thus neither of the two alternative principles can provide a broadband link which can be used for synchronous transmission.